Efficient production of l-phenylalanine catalyzed by a coupled enzymatic system of transaminase and aspartase

A process for efficient production of l-phenylalanine catalyzed by a coupled enzymatic system of transaminase and aspartase with two organisms was developed. One strain, Escherichia coli EP8–10 produces significant transaminase and less aspartase under incubation in the glucose–beef extract medium. In the presence of 50 mg/ml cells of EP8–10, 0.24 mol/l phenylpyruvic acid (PPA) was converted to l-phenylalanine (l-Phe) in 8 h with l-aspartic acid as an amine donor, the conversion rate was 97%. Another strain, E. coli EA-1, a mutant strain of ATCC11303, produces significant aspartase and less transaminase. l-Aspartate (l-Asp), the amine donor, could be produced by EA-1 from fumarate (Fu) and ammonia. In presence of the mixture of EP8–10 and EA-1 cell, l-phenylalanine was efficiently produced from PPA and ammonium fumarate. An optimum reaction condition of the coupled enzymatic system is as follows: the concentration ratio of two cells as 0.4:1 (EA-1 to EP8–10), concentration ratio of two substrates (PPA to Fu) as 1:1.2 (mol). When concentration of PPA was 0.24, 0.233 mol/l (38 g/l), l-phenylalanine acid was accumulated by the conversion rate up to 97%. l-Phenylalanine production is more economical by the coupled enzymatic system, since one of the substrates l-aspartate was replaced by the relative cheap fumaric acid.